JP2009085635A - Handwriting handwriting input system - Google Patents

Abstract

PROBLEM TO BE SOLVED: In a conventional handwritten handwriting input system, when the amplitude of an ultrasonic signal detected by a receiving unit is small, the measurement accuracy of arrival time is lowered, a large amount of memory or high speed is used for waveform data measurement Therefore, a high-resolution A / D converter is required, resulting in high costs.
SOLUTION: A time difference corresponding to a zero cross point stored in a memory before and after an ultrasonic signal exceeds a threshold is set as a reference period, from a zero cross point corresponding to a reference period stored in the memory, Go back by the reference period and continue going back by the reference period until there is no zero crossing point that matches within the specified error at the time that goes back, and the time of the last matching zero crossing point is sent to the ultrasonic signal reception unit of the ultrasonic signal The problem could be solved by setting the arrival time of.
[Selection] Figure 1

Description

  The present invention is a handwriting handwriting input system comprising: an electronic pen that emits at least an infrared signal and an ultrasonic signal; and a means for receiving the infrared signal and the ultrasonic signal and calculating a position coordinate of the electronic pen from the difference in arrival time. The electronic pen transmits an ultrasonic signal, and the time of the zero cross point of the ultrasonic signal received by the infrared ultrasonic measurement unit is sequentially stored, and the arrival time of the ultrasonic signal is appropriately extracted from the stored time. The present invention relates to a handwriting handwriting input system that improves the accuracy of position coordinates of an electronic pen.

2. Description of the Related Art Conventionally, a technique for receiving an ultrasonic signal with high accuracy in detecting the position coordinates of an electronic pen using an infrared signal or an ultrasonic signal is known. For example, in Japanese Unexamined Patent Application Publication No. 2003-222675 (Patent Document 1), an infrared signal and an ultrasonic signal are emitted from a transmission unit, the signals are received by the reception unit, and the transmission unit is based on the arrival time of the ultrasonic signal. When calculating the distance between the receiving unit and the receiving unit, a technique for accurately measuring the arrival time of the ultrasonic signal in the receiving unit and reflecting it in calculating the distance between the transmitting unit and the receiving unit is disclosed.

A handwritten handwriting input system using this distance measurement technique is, for example, as follows. When writing, the ultrasonic signal transmitted from the ultrasonic transmitter mounted on the pen is received by two ultrasonic sensors fixedly arranged, and the coordinate position is measured from the two measured distances. The movement of the pen that accompanies the entry of characters on the keyboard is input to the information processing device. At this time, in order to accurately measure the two distances, a transmission unit that transmits an ultrasonic signal, a reception unit (ultrasonic sensor) that receives at least one ultrasonic signal and converts it into an electrical signal, A timing detector that measures the number of times the received waveform of the ultrasonic signal from the receiver crosses a predetermined threshold, detects a crossing timing after the predetermined number of times from the first crossing point, and an ultrasonic wave by the transmitter It is necessary to provide a time measuring unit that measures the time from the start of transmission to the detected intersection timing, and a distance measuring unit that calculates the distance based on the measured time. The resolution of arrival time measurement using the waveform of the received ultrasonic signal depends on the slope of the waveform that intersects the threshold, and the higher the amplitude, the steeper the slope. As the threshold value is crossed, the variation in timing becomes smaller. Therefore, the measurement accuracy of the propagation time is improved by detecting the timing of crossing with a wave having a large amplitude at which the slope of the waveform crossing the threshold value is steep.
In addition, in order to accurately measure two distances, a transmission unit that transmits an ultrasonic signal, a reception unit (ultrasonic sensor) that receives at least one ultrasonic signal and converts it into an electrical signal, and reception A timing detection unit that measures the number of times that the waveform of the received signal of the ultrasonic signal from the unit intersects a predetermined threshold and detects each intersection timing for a predetermined number of times from the intersection after the predetermined number of times counting from the first intersection And a time measurement unit for calculating a time obtained by adding and averaging each time from the start of transmission of the ultrasonic signal by the transmission unit to each detected intersection timing, and distance measurement for calculating a distance based on the time obtained by the addition average Part. The effective time resolution is further improved by averaging the plurality of intersection timings at which the slope of the waveform that intersects the threshold value is steep.

  In Japanese Patent Laid-Open No. 8-254454 (Patent Document 2), an ultrasonic signal is transmitted to an object to be measured, an ultrasonic signal that is reflected and returned is received, and the ultrasonic signal is transmitted. An apparatus for measuring the time from reception to reception and measuring the distance to the measurement object is disclosed. For reception of this ultrasonic signal, a plurality of peak points appearing in the waveform are detected, and a zero cross point where a virtual envelope connecting these peak points intersects the zero level of the waveform is detected. Then, an elapsed time from the rising edge of the first wave of the transmission waveform of the ultrasonic signal to the zero cross point of the reception waveform is measured, a predetermined offset time is added to the measured value, and the result of the addition is measured. The distance to the measurement object is calculated and the measurement accuracy is improved.

  Similarly, Japanese Patent Laid-Open No. 5-034192 (Patent Document 3) discloses an apparatus for propagating an ultrasonic signal to an object to be measured and measuring the propagation time thereof. In order to calculate the propagation time of the ultrasonic wave received by the ultrasonic wave receiver based on the output timing of the ultrasonic wave signal transmitter, a waveform storage unit for sequentially storing the received ultrasonic signal, and this A zero-cross position detector that detects the zero-cross point from the stored ultrasonic signal waveform data, and calculates the propagation time of the received ultrasonic signal based on the output timing of the zero-cross position detector and the receiver of the ultrasonic signal. And an amplitude ratio calculation function in which the zero cross position detection unit obtains an amplitude ratio between adjacent waves from the waveform data of the ultrasonic signal in the waveform storage unit, and the calculated amplitude ratio. A reference wave selection function that selects waveform data related to the maximum amplitude ratio as a reference wave, and a zero cross point specification function that specifies a zero cross point based on the selected reference wave By Rukoto identifies the zero-cross point of the ultrasonic signal received, and calculates the propagation time of the ultrasonic signal with high accuracy.

JP 2003-222675 A JP-A-8-254454 JP-A-5-034192

In Patent Document 1, when the distance between the transmitting unit that transmits the ultrasonic signal and the receiving unit that receives the ultrasonic signal is far and the overall amplitude is small, the predetermined number of times counted from the first intersection Even if the predetermined number of times of the timing detection unit that detects the later crossing timing is the same, the amplitude of the waveform of the first few ultrasonic signals received is smaller than the threshold, and the waveform after the maximum amplitude waveform can be detected There is sex. For this reason, there is a possibility that the position of the waveform having a large amplitude in the waveform of the ultrasonic signal detected by the receiving unit is changed from the position where it should be, leading to a decrease in accuracy.
In Patent Document 2 and Patent Document 3, when an ultrasonic signal is received, the ultrasonic signal received by the receiver is converted into an electric signal and then amplified by an amplifier. The waveform data of the ultrasonic signal output via is stored. Therefore, a large amount of memory is required, and in order to generate the waveform data, a high-speed and high-resolution A / D converter is required, which may increase the cost and increase the waveform amplitude or peak. In order to perform processing such as extracting points, it is necessary to perform processing using a large amount of waveform data memory, which may take time.

The present invention includes at least an infrared generation circuit including an infrared light emitting element, an ultrasonic generation circuit including an ultrasonic generation element, control means for controlling infrared signals and ultrasonic signals transmitted from these circuits, and a recording medium An electronic pen comprising a writing unit having a function capable of leaving a locus directly on the switch and a switch for determining whether or not the writing unit is in a writing state;
And at least one infrared light receiving unit and two or more ultrasonic wave receiving units, and measuring the arrival of the infrared signal and the ultrasonic signal to the infrared light receiving unit or the ultrasonic wave receiving unit. Calculate the distance between the electronic pen and the ultrasonic receiver using the ultrasonic measurement unit, the arrival time difference between the infrared signal and the ultrasonic signal obtained from the infrared ultrasonic measurement unit, and the speed of sound, A handwriting handwriting input system comprising a coordinate calculation unit that calculates the position coordinate data of the electronic pen using the distance, and a conversion processing unit that has a function of converting the position coordinate data of the electronic pen into handwriting data, The infrared ultrasonic measurement unit measures at least a zero-cross point of rising or falling of the waveform of the ultrasonic signal received by the ultrasonic receiving unit. And an amplitude comparison unit that detects that the amplitude of the waveform of the ultrasonic signal exceeds a predetermined threshold, and the coordinate calculation unit is a time storage unit that sequentially stores the time of the zero cross point; From the zero cross point corresponding to the reference period stored in the time storage unit, the time difference of the time corresponding to the zero cross point before and after the amplitude of the waveform of the ultrasonic signal exceeds a predetermined threshold as a reference period , Going back by the reference period, and going back by the reference period until there is no zero crossing point that matches within a predetermined error at the time pointed back, the time of the zero crossing point that last matched is the The gist of the present invention is a handwritten handwriting input system having means for extracting the time of arrival at an ultrasonic wave reception unit.

The handwriting handwriting input system of the present invention includes a piezo element, an amplifier, a filter circuit, a comparator, a zero-cross circuit, a timer, a memory, a CPU, and the like to receive an ultrasonic signal transmitted from an ultrasonic transmission unit of an electronic pen. Yes.
The ultrasonic signal received by the piezo element is amplified by an amplifier, and noise having an unnecessary frequency is removed by a bandpass filter. When the ultrasonic signal from which noise has been removed passes through the zero cross point, the time at that time is sequentially stored in the memory. Then, using the time difference of the time corresponding to the zero cross point stored in the memory before and after the ultrasonic signal exceeds the threshold as the reference period, from the zero cross point corresponding to the reference period stored in the memory, the reference period Go back by the amount of time, and go back by the reference period until there is no zero crossing point that matches within the specified error at the time of going back, and the time of the last matching zero crossing point arrives at the ultrasonic receiver of the ultrasonic signal. It is time.
As described above, in the present invention, since the arrival time of the ultrasonic signal to the receiver can be extracted regardless of the number of wavelengths of the wave exceeding the amplitude threshold value, the electronic pen and the reception unit can be received. Even when the distance to the machine is far and the overall amplitude is small, the arrival time of the ultrasonic signal can be measured and extracted with high accuracy.
In addition, since it is not necessary to constantly measure the amplitude of the waveform of the ultrasonic signal or to store the waveform data in a memory, a large amount of memory and a high-speed, high-resolution A / D converter are not required. There is no fear of incurring high.
Furthermore, power consumption is reduced, and a dry battery can be used as a power source, and it can also be used on a mobile.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, a preferred embodiment of a handwriting handwriting input system according to the invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a perspective view showing an example of a handwritten handwriting input system according to the present embodiment. In the figure, a receiver 2 includes two ultrasonic receiving units, an infrared ultrasonic measuring unit having an infrared receiving unit and a receiving circuit, a coordinate calculation unit for calculating position coordinate data of an electronic pen, and handwriting the position coordinate data. Consists of components of a conversion processing unit that converts data. The receiver 2 is connected to the computer 6 via the communication interface 5, and the handwriting data of the electronic pen 1 is transmitted from the conversion processing unit of the receiver 2 to the computer 6, so that the computer 6 is mounted on the mounted display. A handwriting can be displayed, a character recognition process can be performed, or it can be stored in a storage device.

The structure of the electronic pen 1 will be described with reference to the block diagram of the electronic pen in FIG. The basic configuration of the electronic pen 1 includes an ultrasonic generation circuit 11 that can transmit an ultrasonic signal by the ultrasonic generation element 10, an infrared generation circuit 9 that transmits an infrared signal from the infrared light emitting element 8, and an ultrasonic wave. A signal transmission unit 13 including a control means for controlling the signal and the infrared signal to be transmitted at regular intervals, the writing unit 3 of the pen tip, and the writing unit 3 while contacting the recording medium 4, characters and drawings The pen switch 14 that is turned on / off in accordance with the writing state and the non-writing state when drawing, and the entire electronic pen so that it can be used in a wireless manner in consideration of portability and ease of writing It consists of a battery 15 that supplies power. In the present embodiment, the writing unit 3 is a ballpoint pen or a mechanical pencil provided with a function capable of directly leaving a locus on the recording medium 4. For example, the writing unit 3 has a built-in stylus and the surface of the display. Any surface including the above may be used as a writing medium.

A capacitor, a coil, and an ultrasonic generation element 10 are disposed inside the ultrasonic generation circuit 11, and a piezoelectric element is used as the ultrasonic generation element 10. The shape of this piezo element is often cylindrical. This is because it is preferable that the piezo element of the electronic pen 1 transmits an ultrasonic signal uniformly in any direction on the recording medium 4 regardless of the direction in which the writer uses the electronic pen 1. It is. In this configuration, the cylindrical piezo element itself also has a resonance frequency. At this time, the resonance frequency f ₀ of the LC resonance circuit of the ultrasonic wave generation circuit 11 is preferably adjusted as close as possible to the resonance frequency of the piezoelectric element by adjusting the circuit configuration. The resonance frequency of a piezo element is determined by the characteristics of the piezo film and the diameter of the cylinder, and the ultrasonic wave has a lower attenuation with distance, while the higher the frequency, the higher the coordinate resolution. To determine the resonance frequency. In the case of a handwritten handwriting input system using an electronic pen, the frequency is preferably about several tens of kHz, and around 80 kHz is preferably used.

A transistor or FET and an infrared light emitting element 8 are arranged inside the infrared generation circuit 9, and light emission of the infrared light emitting element 8 can be turned on or off by controlling the transistor or FET. At this time, it is preferable to arrange a plurality of infrared light emitting elements 8 in consideration of the directivity angle of the infrared light emitting element 8 so as to emit infrared light in all directions with respect to the cylindrical axis of the electronic pen 1.

Next, the structure of the receiver 2 will be described with reference to an internal block diagram of the receiver of FIG. The receiver 2 includes an infrared light receiving unit 30, ultrasonic receiving units 31 and 32, an amplifier 33, a filter circuit unit 36, and a comparator 39, an amplifier 34, a filter circuit unit 37, a comparator 40, and a zero cross. An infrared ultrasonic measurement unit 42 including an ultrasonic reception circuit 53 including a circuit 26, an amplifier 35, a filter circuit unit 38, a comparator 41, and an ultrasonic reception circuit 53 including a zero cross circuit 27, a CPU 43, a timer 44, and a flash memory. 45, a coordinate calculation unit 47 including a RAM 46, a conversion processing unit 50 including a CPU 48 and a RAM 49, a communication interface 5 for connecting to the computer 6, and a battery 51 capable of supplying power to the entire receiver 2. ing. It is better to install the ultrasonic receiving circuits 53 and 54 as many as the number of ultrasonic receiving units so that the ultrasonic receiving units 3 1 and 32 can perform processing even if they simultaneously receive ultrasonic signals. In the present embodiment, the coordinate calculation unit 47 and the conversion processing unit 50 are described separately by function, but the CPU and RAM of the coordinate calculation unit 47 and the conversion processing unit 50 may be common.

The ultrasonic receivers 31 and 32 are configured with the same piezoelectric elements inside the ultrasonic generator circuit 11 of the electronic pen 1 and receive ultrasonic signals transmitted from the ultrasonic generator circuit 11. is there. The receiver 2 is provided with an opening so that an ultrasonic signal transmitted from the electronic pen 1 can be received without being blocked.
The infrared light receiving unit 30 is provided with an infrared light receiving element and receives an infrared signal emitted from the infrared light emitting element 8 of the infrared generation circuit 12 of the electronic pen 1. Therefore, the wavelength of the infrared light receiving element is desirably the same as that of the infrared light emitting element 8.

Infrared signal reception will be described. The infrared signal received by the infrared light receiving unit 30 is amplified by the amplifier 33 and sent to the filter circuit unit 36. The filter circuit unit 36 is preferably a filter that allows a signal in the same frequency band as the infrared signal received by the electronic pen 1 to pass through the external noise so that the external noise can be blocked even when the external noise is received. For example, when the wavelength of the infrared light emitting element 8 of the electronic pen 1 is 940 nm, a band pass filter having a peak at a wavelength of 940 nm may be designed. Thereafter, when the comparator 39 receives a signal that is equal to or greater than a predetermined threshold, the CPU 43 of the coordinate calculation unit 47 reads the time at that time from the timer 44 when the comparator 39 detects the signal, and this time is read as an infrared ray. The signal is stored in the RAM 46 as the arrival time of the signal.
Thereafter, when the comparator 39 detects the reception of a signal equal to or greater than a specific threshold, the CPU 43 of the coordinate calculation unit 47 reads the time when the signal reception is detected from the timer 44 and uses this time as the arrival time of the infrared signal in the RAM 46. Save to. When the comparator 39 detects reception of a signal that is equal to or greater than a specific threshold, the arrival time of the infrared signal is determined even if reception of the first waveform of the infrared signal cannot be performed. This is because the speed of the infrared signal from the pen 1 is much faster than the speed of the ultrasonic signal, so that one waveform of the infrared signal can be determined to be within the error.

Next, the ultrasonic signals transmitted from the electronic pen 1 are received by the two ultrasonic receivers 31 and 32. Here, since the circuit configurations of the ultrasonic receiving circuits 53 and 54 are the same, description will be given using the ultrasonic receiving unit 31 and the ultrasonic receiving circuit 53. The ultrasonic receiver 31 receives the ultrasonic signal, the amplifier 33 amplifies the signal, the filter circuit 35 removes the external noise, and then the zero cross circuit 26 rises or falls the zero cross point. When the zero crossing circuit 26 measures the rising or falling zero crossing point of the signal, the CPU 43 of the coordinate calculation unit 47 reads the time at that time from the timer 44 and uses this as the time of the zero crossing point. Save in RAM 46. This is repeated and the time of the zero cross point is sequentially stored in the RAM 46 each time. Here, after removing the external noise by the filter circuit unit 35, when the comparator 40 detects reception of a signal equal to or greater than a predetermined threshold value, the CPU 43 of the coordinate calculation unit 47 determines the next zero cross point by the zero cross circuit 26. After measuring and saving the time of the zero cross point in the RAM 46, the sequential saving operation is terminated. The CPU 43 of the coordinate calculation unit 47 uses the time difference of the time corresponding to the zero cross point stored in the RAM 46 before and after the amplitude of the waveform of the ultrasonic signal in the comparator 40 exceeds a predetermined threshold as a reference period, and stores it in the RAM 46. Go back from the zero-cross point corresponding to the memorized reference cycle by the reference cycle, and keep going back by the reference cycle until there is no zero-cross point that matches the retroactive time within the specified error. The point time is extracted as the arrival time of the ultrasonic signal to the ultrasonic receiving unit. Since the component variation in the ultrasonic wave generation circuit 11 of the electronic pen 1 is ± 10%, the predetermined error is within ± 20% of the resonance frequency of the electronic pen 1, and preferably within ± 10%.

Then, the CPU 43 of the coordinate calculation unit 47 determines the arrival time difference between the arrival time of the infrared signal in the infrared light receiving unit 30 stored in the RAM 46 and the arrival time of the ultrasonic signal in the two ultrasonic reception units 31 and 32 and the sound speed. Is used to calculate the distance from the electronic pen 1 to the ultrasonic receivers 31 and 32. The position coordinates of the electronic pen 1 are calculated using the theory of trigonometry, assuming a triangle with the positions of the electronic pen 1 and the two ultrasonic receivers 31 and 32 as vertices. The CPU 43 stores the calculated position coordinate data of the electronic pen 1 in the RAM 49 of the conversion processing unit 50. In addition, when the computer 6 is connected via the communication interface 5, the content stored in the RAM 49 of the conversion processing unit 50 can be transmitted to the computer 6.

FIG. 4 shows the waveform generated by the zero-cross circuit using the measured waveform after the received ultrasonic signal is amplified by the amplifier and filtered by the filter circuit, the threshold value α set in the comparator, and the measured waveform. It is a figure. When the measurement waveform is positive, a positive signal is generated from the zero-cross circuit, and the waveform is output after being converted into a digital signal so that a signal of 0 V is generated otherwise. The rise of the digital signal, that is, the rise of the ultrasonic signal is set as a zero cross point, and the time of the timer at this time is stored in the RAM. Further, the time difference between times t3 and t4 corresponding to the zero cross points before and after the measured waveform exceeds the threshold value α of the comparator is defined as a reference period dt3, which corresponds to the reference period dt3 and the reference period dt3 stored in the RAM. It goes back from the zero crossing point by the reference period dt3, and keeps going back by the reference period until there is no zero crossing point that coincides with the retroactive time within a predetermined error. In this case, a time t2 exists as a zero cross point that coincides within a predetermined error with a time t3-dt3 when the reference period dt3 is subtracted with respect to the time t3 that is the older of the reference period dt3. Furthermore, time t1 exists as a zero cross point that coincides with time t2-dt3 obtained by subtracting the reference period dt3 from time t2 within a predetermined error. Similarly, there is no zero-cross point that coincides within a predetermined error at time t1-dt3 when the reference period dt3 is subtracted from time t1. Thus, the time t1 is extracted as the arrival time of the ultrasonic signal. That is, from the zero-cross point corresponding to the reference cycle and the reference cycle stored in the RAM, the zero-cross point that goes back by the reference cycle with respect to the newly existing zero-cross point and coincides with the retroactive time within a predetermined error. Until it no longer exists, it keeps going back by the reference period, and the time of the zero cross point that finally matched is extracted as the arrival time of the ultrasonic signal.

Another extraction method is as follows. A time t2 exists as a zero cross point that coincides within a predetermined error with a time t3-dt3 × 1 when the reference period dt3 is subtracted with respect to the time t3 that is the older of the reference period dt3. Furthermore, time t1 exists as a zero cross point that coincides with time t3-dt3 × 2 within a predetermined error when the reference period dt3 is subtracted from time t3-dt3 × 1. Similarly, there is no zero cross point that coincides within a predetermined error at time t3-dt3 × 3 when the reference period dt3 is subtracted from time t3-dt3 × 2. Thus, the time t1 is extracted as the arrival time of the ultrasonic signal. That is, the reference period and the zero-cross point corresponding to the reference period stored in the RAM are traced back N times of the reference period from the time of the old zero-cross point of the reference period, and match the retroactive time within a predetermined error. Until the zero cross point no longer exists, it continues going back by the reference period, and the time of the last matched zero cross point is extracted as the arrival time of the ultrasonic signal.

FIG. 5 shows a waveform generated by a zero-cross circuit using a measured waveform after the received ultrasonic signal is amplified by an amplifier and filtered by a filter circuit, a threshold value α set in a comparator, and the measured waveform. FIG. The difference from FIG. 4 is that the waveform is output after being converted into a digital signal so that a positive signal is generated from the zero cross circuit when the measured waveform is negative, and a signal of 0 V is generated otherwise. The rising edge of the digital signal, that is, the falling edge of the ultrasonic signal is set as a zero cross point, and the timer time at this time is stored in the RAM. Further, a time difference between times t3 ′ and t4 ′ corresponding to the zero cross points before and after the measured waveform exceeds the threshold value α of the comparator is set as a reference period dt3 ′, and the reference period dt3 ′ and a reference stored in the RAM It goes back by the reference period dt3 ′ from the zero cross point corresponding to the period dt3 ′, and keeps going back by the reference period until there is no zero cross point that coincides with the retroactive time within a predetermined error. In this case, the time t2 ′ is a zero-crossing point that coincides with a time t3′−dt3 ′ obtained by subtracting the reference period dt3 ′ within a predetermined error with respect to the time t3 ′ that is the older of the reference period dt3 ′. Exists. Further, a time t1 'exists as a zero cross point that coincides within a predetermined error with a time t2'-dt3' obtained by subtracting the reference period dt3 'from the time t2'. Similarly, there is no zero cross point that coincides within a predetermined error at time t1'-dt3 'when the reference period dt3' is subtracted from time t1 '. Thus, the time t1 'is extracted as the arrival time of the ultrasonic signal. That is, the zero-cross point that goes back from the zero-cross point corresponding to the reference cycle and the reference cycle stored in the RAM by the reference cycle with respect to the newly existing zero-cross point, and that coincides within a predetermined error at the traced time. Until it no longer exists, it keeps going back by the reference period, and the time of the zero cross point that finally matched is extracted as the arrival time of the ultrasonic signal.

Another extraction method is as follows. Time t2 ′ exists as a zero-crossing point that coincides within a predetermined error with time t3′−dt3 ′ × 1 when the reference period dt3 ′ is subtracted with respect to the time t3 ′ that is the older of the reference period dt3 ′. To do. Further, a time t1 'exists as a zero cross point that coincides with a time t3'-dt3'x2 within a predetermined error when the reference period dt3' is subtracted from the time t3'-dt3'x1. Similarly, there is no zero cross point that coincides within a predetermined error at time t3'-dt3'x3 when the reference period dt3 'is subtracted from time t3'-dt3'x2. Thus, the time t1 'is extracted as the arrival time of the ultrasonic signal. That is, the reference period and the zero-cross point corresponding to the reference period stored in the RAM are traced back by N periods of the reference period from the time of the zero-cross point of the old reference period, and coincide with the retroactive time within a predetermined error. Until the zero cross point no longer exists, it continues going back by the reference period, and the time of the last matched zero cross point is extracted as the arrival time of the ultrasonic signal.

Here, processing when noise for one cycle is mixed in the measurement waveform of the ultrasonic signal shown in FIG. 4 will be described with reference to FIG. It is the figure which showed the waveform produced | generated in a zero cross circuit using the measured waveform after amplifying the received ultrasonic signal with an amplifier and filtering with the filter circuit, the threshold value (alpha) set to the comparator, and a measured waveform . Noise having a period longer or shorter than the period of the resonance frequency of 80 kHz of the ultrasonic signal oscillated from the ultrasonic wave generation circuit 11 of the electronic pen 1 is removed as unnecessary frequency noise by the filter circuit. However, in consideration of variations in the resonance frequency of the ultrasonic signal of the ultrasonic wave generation circuit 11 of the electronic pen 1, a certain frequency band is provided, so that a signal having a period of 80 kHz passes through the filter circuit. Therefore, the noise for one period of the period de1 close to the period of 80 kHz passes through the filter circuit together with the ultrasonic signal. Then, when the noise of the cycle de1 after passing through the filter circuit and the waveform of the ultrasonic signal are positive, a positive signal is generated from the zero cross circuit, and the waveform is converted to a digital signal so that a signal of 0 V is generated otherwise. Output. The rise of the digital signal, that is, the rise of the ultrasonic signal is set as a zero cross point, and the time of the timer at this time is stored in the RAM.
In addition, the time difference between times t3 and t4 corresponding to the zero-cross point before and after the waveform of the ultrasonic signal that has passed through the filter circuit exceeds the threshold value α of the comparator is defined as a reference period dt3, and is stored in the RAM. It goes back by the reference period dt3 from the zero-cross point corresponding to the reference period dt3, and keeps going back by the reference period until there is no zero-cross point that coincides within a predetermined error at the traced time. In this case, a time t2 exists as a zero cross point that coincides within a predetermined error with a time t3-dt3 when the reference period dt3 is subtracted with respect to the time t3 that is the older of the reference period dt3. Furthermore, time t1 exists as a zero cross point that coincides with time t2-dt3 obtained by subtracting the reference period dt3 from time t2 within a predetermined error. Similarly, there is no zero cross point that coincides within a predetermined error at time t1-dt3 when the reference period dt3 is subtracted from time t1. Although a zero cross point exists at the time e1, it does not coincide with the time t1-dt3 within a predetermined error, so the time t1 is extracted as the arrival time of the ultrasonic signal. That is, the zero-cross point that goes back from the zero-cross point corresponding to the reference cycle and the reference cycle stored in the RAM by the reference cycle with respect to the newly existing zero-cross point, and that coincides within a predetermined error at the traced time. Until it no longer exists, it keeps going back by the reference period, and the time of the zero cross point that finally matched is extracted as the arrival time of the ultrasonic signal.

Another extraction method is as follows. A time t2 exists as a zero cross point that coincides within a predetermined error with a time t3-dt3 × 1 when the reference period dt3 is subtracted with respect to the time t3 that is the older of the reference period dt3. Furthermore, time t1 exists as a zero cross point that coincides with time t3-dt3 × 2 within a predetermined error when the reference period dt3 is subtracted from time t3-dt3 × 1. Similarly, there is no zero cross point that coincides within a predetermined error at time t3-dt3 × 3 when the reference period dt3 is subtracted from time t3-dt3 × 2. Although a zero cross point exists at the time e1, it does not match the time t3-dt3 × 3 within a predetermined error, so the time t1 is extracted as the arrival time of the ultrasonic signal. That is, the reference period and the zero-cross point corresponding to the reference period stored in the RAM are traced back N times of the reference period from the time of the old zero-cross point of the reference period, and match the retroactive time within a predetermined error. Until the zero cross point no longer exists, it continues going back by the reference period, and the time of the last matched zero cross point is extracted as the arrival time of the ultrasonic signal.

  In FIGS. 4 and 5, it is necessary to use properly when it is known in advance whether the first waveform of the ultrasonic signal is on the plus side or the minus side. The two types of waveforms described in FIG. 5 are output, the arrival time of the ultrasonic signal is extracted from each of the two types of waveforms, and the arrival time of the ultrasonic signal having the two types of waveforms is earlier. Can be extracted as the arrival time of the ultrasonic signal. Thereby, the arrival time of an ultrasonic signal with accuracy can be measured, and as a result, the position coordinate of the electronic pen 1 can be measured with accuracy.

Hereinafter, the present invention will be described with reference to examples and comparative examples. The present invention is not limited to the following examples, and includes various modifications within the technical scope of the present invention.
Example 1
The handwriting handwriting input system arranged as shown in FIG. 1 was used. However, the frequency of the ultrasonic signal of the ultrasonic generation circuit 11 of the electronic pen 1 is set to 80 kHz, the infrared wavelength of the infrared generation circuit is set to 940 nm, and the transmission interval of the ultrasonic signal and the infrared signal of the signal transmission unit 13 is 100. It was set to be times / second. Further, the receiver 2 has the configuration shown in the block diagram of FIG. 3, and the ultrasonic signal received from the electronic pen 1 is a waveform in which the first waveform of the ultrasonic signal is on the plus side, and the block of FIG. The waveforms output from the zero-cross circuits 28 and 29 in the figure are the waveforms shown in FIG. The filter circuit units 37 and 38 are band-pass filters having a peak at 80 kHz, and the filter circuit unit 33 is a band-pass filter having a peak at a wavelength of 940 nm. The receiver 2 and the computer 6 were disconnected, and the receiver 2 was used using the power of the internal battery 51. The method of extracting the arrival time of the ultrasonic signal is based on the reference period and the zero-cross point corresponding to the reference period stored in the RAM, by going back to the existing zero-cross point by the reference period, A method is used in which the time of the last matching zero-cross point is extracted as the arrival time of the ultrasonic signal until the zero-cross point that matches within a predetermined error no longer exists until the reference period.
The electronic pen 1 was fixedly installed at a position of about 300 mm equally from the two ultrasonic receiving units, and the position coordinate was measured by the receiver 2 while the electronic pen was in a stationary writing state for about 2 seconds. As a result of evaluating the position coordinate data generated by the coordinate calculation unit 47 when this operation was repeated 10 times while changing the position, the position coordinates of the electronic pen could be detected accurately all 10 times.

(Example 2)
The configuration was the same as that of Example 1 except for the method of extracting the ultrasonic signal.
As a method of extracting the arrival time of the ultrasonic signal, the reference period and the zero-cross point corresponding to the reference period stored in the RAM are traced back by N periods of the reference period from the time of the old zero-cross point of the reference period, A method of extracting the time of the last zero cross point that coincides with the reference period and extracting it as the arrival time of the ultrasonic signal is used until there is no zero cross point that coincides with the retroactive time within a predetermined error.
The same test as in Example 1 was performed using the system in Example 1 above. As a result, it was confirmed that the position coordinates of the electronic pen could be accurately detected 10 times, and the same result as in Example 1 was obtained.

(Example 3)
The receiver 2 has the configuration shown in the block diagram of FIG. 6, outputs the two types of waveforms a and b shown in FIG. 7 from the zero-cross circuits 28 and 29, and generates ultrasonic waves from each of the two types of waveforms. The configuration is the same as that of the first embodiment except that the arrival time of the signal is extracted, and the arrival time of the ultrasonic signal having two types of waveforms is extracted as the arrival time of the ultrasonic signal. Similar evaluations were made.
As a result, it was confirmed that the position coordinates of the electronic pen could be accurately detected 10 times, and the same result as in Example 1 was obtained.

Example 4
The configuration was the same as in Example 1 except that one waveform of 100 kHz noise was mixed in the ultrasonic signal.
Evaluation similar to Example 1 was performed using the system of Example 1 described above. As a result, as shown in FIG. 11, the noise period de1 can be removed, and the position coordinates of the electronic pen can be accurately detected 10 times, and it was confirmed that the same result as in Example 1 was obtained. .

(Comparative Example 1)
The receiver 2 has the same configuration as that of the first embodiment except that the receiver 2 has the configuration shown in the block diagram of FIG. 8, does not use the zero cross circuit, and the threshold values of the comparators 40 and 41 are set to a value β smaller than the threshold value α. did.
In the block diagram of FIG. 8, the ultrasonic receiving unit 31 and the ultrasonic receiving circuit 53 and the ultrasonic receiving unit 32 and the ultrasonic receiving circuit 54 operate in the same manner, and therefore the ultrasonic receiving unit 31 and the ultrasonic receiving circuit 53. The extraction of the arrival time of the ultrasonic signal when the comparator 40 is used will be described.
After the ultrasonic signal received by the ultrasonic receiving unit 31 is amplified by the amplifier 34 and the external noise is removed by the filter circuit 37, a positive signal is output from the comparator 40 when the measured waveform of the signal is larger than the threshold value β. In other cases, the signal is converted into a digital signal so that a 0 V signal is generated, and a waveform is output. When the signal rises, the CPU 43 of the coordinate calculation unit 47 stores the time of the timer 43 in the RAM 46. Then, the time of the first ultrasonic signal stored in the RAM 46 is extracted as the arrival time of the ultrasonic signal to the ultrasonic receiving unit 31.
Evaluation similar to Example 1 was performed using the system of Comparative Example 1 described above. As a result, as shown in FIG. 9, about one wavelength of the first ultrasonic signal corresponding to the time T1 of the comparator 40 was dropped, so that the position coordinates of the electronic pen could not be detected accurately.

(Comparative Example 2)
The comparators 40 and 41 have the same configuration as that of the comparative example 1 except that the threshold value γ is closer to 0V than β.
Evaluation similar to Example 1 was performed using the system of Comparative Example 1 described above. As a result, as shown in FIG. 10, a delay of the first ultrasonic signal corresponding to the time ΔT of the comparator 40 occurred, and the position coordinates of the electronic pen could not be detected accurately.

(Comparative Example 3)
The configuration was the same as that of Comparative Example 1 except that one waveform of 100 kHz noise was mixed in the ultrasonic signal.
Evaluation similar to Example 1 was performed using the system of Comparative Example 1 described above. As a result, as shown in FIG. 12, the advance of the first ultrasonic signal corresponding to the time ΔT ′ of the comparator 40 occurs due to the influence of noise, and the position coordinates of the electronic pen could not be detected accurately. .

As described above, each of the first, second, third, fourth, comparative, first, second, and third examples has a relatively simple circuit configuration for measuring the arrival time of the ultrasonic signal. It is simple and the storage capacity of the RAM used for measurement is small. However, compared with Comparative Example 1, Comparative Example 2, and Comparative Example 3, in Example 1, Example 2, Example 3, and Example 4, the arrival of the ultrasonic signal from the time of the zero cross point stored in the RAM. Since the time extraction method is used, the position coordinates of the electronic pen can be accurately detected. Therefore, it was confirmed that the present invention is effective in terms of storage capacity and accuracy of position coordinates in the handwriting handwriting input system.

Perspective view of handwriting handwriting input system Electronic pen block diagram Block diagram of a receiver in an embodiment Conceptual diagram of measurement waveform of ultrasonic signal in the embodiment Conceptual diagram of measurement waveform of another ultrasonic signal in the embodiment Block diagram of another receiver in the embodiment Conceptual diagram of measurement waveform of another ultrasonic signal in the embodiment Block diagram of receiver in comparative example Conceptual diagram of measurement waveform of ultrasonic signal in comparative example Conceptual diagram of the measurement waveform of another ultrasonic signal in the comparative example Conceptual diagram of measurement waveform of another ultrasonic signal in the embodiment Conceptual diagram of the measurement waveform of another ultrasonic signal in the comparative example

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electronic pen 2 Receiver 3 Writing part 4 Recording medium 5 Communication interface 6 Computer 8 Infrared light emitting element 9 Infrared generating circuit 10 Ultrasonic generating element 11 Ultrasonic generating circuit 13 Signal transmission part 14 Pen switch 15, 51 Battery 26, 27 Comparator 28, 29 Zero cross circuit 30 Infrared light receiver 31, 32 Ultrasonic receiver 33, 34, 35 Amplifier 36, 37, 38 Filter circuit 39, 40, 41 Comparator 42 Infrared ultrasonic measurement unit 43, 48 CPU
44 Timer 45 Flash memory 46, 49 RAM
47 Coordinate calculation unit 50 Conversion processing unit 52 Infrared light receiving circuit 53, 54 Ultrasonic wave receiving circuit

Claims (1)

At least an infrared generating circuit including an infrared light emitting element, an ultrasonic generating circuit including an ultrasonic generating element, a control means for controlling infrared signals and ultrasonic signals transmitted from these circuits, and a locus directly on the recording medium An electronic pen consisting of a writing part having a function capable of leaving a mark, a switch for determining whether or not the writing part is in a writing state, at least one infrared receiving part, and two or more Obtained from an infrared ultrasonic measurement unit having an ultrasonic reception unit and measuring the arrival of the infrared signal and the ultrasonic signal to the infrared light receiving unit or the ultrasonic reception unit, and the infrared ultrasonic measurement unit The distance between the electronic pen and the ultrasonic receiver is calculated using the arrival time difference and the sound speed of the infrared signal and the ultrasonic signal, and the position coordinate data of the electronic pen is calculated using the distance. Coordinate calculation unit, and a handwritten input system comprising a conversion processing unit having a function of converting the position coordinate data of the electronic pen on the handwriting data,
The infrared ultrasonic measurement unit includes at least a zero cross detection unit that measures a rising or falling zero cross point of a waveform of an ultrasonic signal received by the ultrasonic receiving unit, and an amplitude of the waveform of the ultrasonic signal. An amplitude comparison unit that detects that a predetermined threshold has been exceeded,
The coordinate calculation unit includes a time storage unit that sequentially stores the time of the zero cross point, and a time difference between times corresponding to the zero cross points before and after the amplitude of the waveform of the ultrasonic signal exceeds a predetermined threshold. The reference period until the zero-cross point corresponding to the reference period stored in the time storage unit is traced back by the reference period and no matching zero-cross point exists within a predetermined error. And a means for extracting the time of the zero-crossing point that coincides with the last time as the arrival time of the ultrasonic signal to the ultrasonic receiving unit.

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